From 0ad5fea2a06952e9f1c5dcf10bd08ef9404fcad1 Mon Sep 17 00:00:00 2001
From: Danny Willems <be.danny.willems@gmail.com>
Date: Wed, 20 Nov 2024 16:47:06 +0100
Subject: [PATCH 1/2] o1vm/riscv32: implement mod_signed

It will be used to implement MInstruction::Rem in a follow-up PR.
---
 o1vm/src/interpreters/riscv32im/constraints.rs |  9 +++++++++
 o1vm/src/interpreters/riscv32im/interpreter.rs | 14 ++++++++++++++
 o1vm/src/interpreters/riscv32im/witness.rs     | 14 ++++++++++++++
 3 files changed, 37 insertions(+)

diff --git a/o1vm/src/interpreters/riscv32im/constraints.rs b/o1vm/src/interpreters/riscv32im/constraints.rs
index 5f8236aed7..67bfa46fea 100644
--- a/o1vm/src/interpreters/riscv32im/constraints.rs
+++ b/o1vm/src/interpreters/riscv32im/constraints.rs
@@ -353,6 +353,15 @@ impl<Fp: Field> InterpreterEnv for Env<Fp> {
         self.variable(position)
     }
 
+    unsafe fn mod_signed(
+        &mut self,
+        _x: &Self::Variable,
+        _y: &Self::Variable,
+        position: Self::Position,
+    ) -> Self::Variable {
+        self.variable(position)
+    }
+
     unsafe fn mul_lo(
         &mut self,
         _x: &Self::Variable,
diff --git a/o1vm/src/interpreters/riscv32im/interpreter.rs b/o1vm/src/interpreters/riscv32im/interpreter.rs
index 438abaa065..7e0826abad 100644
--- a/o1vm/src/interpreters/riscv32im/interpreter.rs
+++ b/o1vm/src/interpreters/riscv32im/interpreter.rs
@@ -1271,6 +1271,20 @@ pub trait InterpreterEnv {
         position: Self::Position,
     ) -> Self::Variable;
 
+    /// Returns `x % y`, storing the results in `position`.
+    ///
+    /// # Safety
+    ///
+    /// There are no constraints on the returned values; callers must manually add constraints to
+    /// ensure that the pair of returned values correspond to the given values `x` and `y`, and
+    /// that they fall within the desired range.
+    unsafe fn mod_signed(
+        &mut self,
+        x: &Self::Variable,
+        y: &Self::Variable,
+        position: Self::Position,
+    ) -> Self::Variable;
+
     /// Returns `(x / y, x % y)`, storing the results in `position_quotient` and
     /// `position_remainder` respectively.
     ///
diff --git a/o1vm/src/interpreters/riscv32im/witness.rs b/o1vm/src/interpreters/riscv32im/witness.rs
index 895ab46e1c..6c87d64b8e 100644
--- a/o1vm/src/interpreters/riscv32im/witness.rs
+++ b/o1vm/src/interpreters/riscv32im/witness.rs
@@ -515,6 +515,20 @@ impl<Fp: Field> InterpreterEnv for Env<Fp> {
         res
     }
 
+    unsafe fn mod_signed(
+        &mut self,
+        x: &Self::Variable,
+        y: &Self::Variable,
+        position: Self::Position,
+    ) -> Self::Variable {
+        let x: u32 = (*x).try_into().unwrap();
+        let y: u32 = (*y).try_into().unwrap();
+        let res = ((x as i32) % (y as i32)) as u32;
+        let res = res as u64;
+        self.write_column(position, res);
+        res
+    }
+
     unsafe fn divmod_signed(
         &mut self,
         x: &Self::Variable,

From 4e0220dbd6c09aaff3578d8f8a3f322674f4c9f4 Mon Sep 17 00:00:00 2001
From: Danny Willems <be.danny.willems@gmail.com>
Date: Mon, 25 Nov 2024 10:57:40 +0100
Subject: [PATCH 2/2] o1vm/riscv32im: simplify mod_signed

---
 o1vm/src/interpreters/riscv32im/witness.rs | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/o1vm/src/interpreters/riscv32im/witness.rs b/o1vm/src/interpreters/riscv32im/witness.rs
index 6c87d64b8e..bb0e0cf6c5 100644
--- a/o1vm/src/interpreters/riscv32im/witness.rs
+++ b/o1vm/src/interpreters/riscv32im/witness.rs
@@ -521,9 +521,9 @@ impl<Fp: Field> InterpreterEnv for Env<Fp> {
         y: &Self::Variable,
         position: Self::Position,
     ) -> Self::Variable {
-        let x: u32 = (*x).try_into().unwrap();
-        let y: u32 = (*y).try_into().unwrap();
-        let res = ((x as i32) % (y as i32)) as u32;
+        let x: i32 = (*x).try_into().unwrap();
+        let y: i32 = (*y).try_into().unwrap();
+        let res = (x % y) as u32;
         let res = res as u64;
         self.write_column(position, res);
         res